Electrochemical Partial Oxidation of Methane in Solid Oxide Fuel Cells: Effect of Anode Reforming Activity
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Electrochemical Partial Oxidation of Methane in Solid Oxide Fuel Cells: Effect of Anode Reforming Activity Manoj R. Pillai Æ David M. Bierschenk Æ Scott A. Barnett
Received: 27 August 2007 / Accepted: 15 October 2007 / Published online: 30 October 2007 Ó Springer Science+Business Media, LLC 2007
Abstract Direct-methane solid oxide fuel cells were used to produce electricity and syngas. During initial operation at 750 °C, the cells produced 0.9 W/cm2 and &90% methane conversion to syngas at a rate of 30 sccm/cm2. However, the methane conversion decreased continuously over the first 30–40 h of operation, even though the solid oxide fuel cells (SOFC) electrical performance was stable. An additional catalyst layer on the anode yielded more stable methane conversion to syngas. Keywords Solid oxide fuel cells (SOFC) Electrochemical partial oxidation (EPOx) Syngas Methane Ni-YSZ
1 Introduction Direct-methane solid oxide fuel cells (SOFCs) can produce syngas by reacting methane with oxygen transported across
M. R. Pillai (&) D. M. Bierschenk S. A. Barnett Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA e-mail: [email protected] D. M. Bierschenk e-mail: [email protected] S. A. Barnett e-mail: [email protected] Present Address: M. R. Pillai Functional Coating Technology LLC, 1801 Maple Avenue, Suite 5320, Evanston, IL 60201, USA
the electrolyte, a process termed electrochemical partial oxidation (EPOx) [1–7]. Syngas is an important precursor to hydrogen and synthetic liquid chemicals/fuels including methanol and various hydrocarbons [8–10]. Advantages/ disadvantages of EPOx compared with other reforming methods have been described previously [1]. Key potential advantages are similar to those for ceramic membrane reactors: production of syngas without nitrogen dilution and reduced cost due to process intensification by combining the oxygen separation and partial oxidation steps. SOFCs have the additional advantage of producing two valuable products—syngas and electricity—which can significantly improve economics [1]. Most prior reports on EPOx have utilized SOFCs with relatively low power densities and thus low syngas production rates. Recently, high-rate production of syngas (20 sccm/cm2) along with high electrical power density (0.7 W/cm2) at 750 °C was demonstrated using conventional Ni-YSZ anode-supported SOFCs [1]. Stable SOFC electrical output was reported for up to 300 h, but the chemical products were not measured versus time. In this letter, we describe detailed results on the electrical output and chemical products versus time from direct-methane anode-supported SOFCs. During the early stages of operation, the SOFC reactor product composition was nearly equal to that expected at equilibrium. However, the methane conversion and syngas production rate decreased continuously over the first 30–40 h of operation. This was explained by a rapid decrease in reforming activity that has recently been reported for Ni-YSZ anodes [11], given tha
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